Passive intermodulation detection

ABSTRACT

A method, apparatus and receiver for detecting intermodulation distortion (IMD) affecting a received signal in a wireless receiver are provided. One method includes determining a measurement indicative of IMD based on at least one transmit signal. When the measurement indicative of IMD exceeds a first pre-determined level, at least one sample of an amplitude of a signal output by the wireless receiver is collected in a first data set. When the measurement indicative of intermodulation distortion does not exceed a second pre-determined level, the second predetermined level being less than the first predetermined level, at least one sample of an amplitude of the signal output by the wireless receiver is collected in a second data set. A comparison is performed based on data of the first data set and on data of the second data set to determine a measure of IMD.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.14/384,258, filed Sep. 10, 2014, entitled PASSIVE INTERMODULATIONDETECTION, which is a U.S. National Stage Application ofPCT/IB2014/061141, filed May 1, 2014, entitled PASSIVE INTERMODULATIONDETECTION, the entirety of which both are incorporated herein byreference.

TECHNICAL FIELD

The embodiments described herein relate to wireless communications andin particular to a method and system for determining an extent ofintermodulation distortion in a wireless receiver.

BACKGROUND

Passive intermodulation (PIM) occurs when signals are present in apassive device that exhibits some non-linear behavior. In a basestation, such as an evolved node B (eNB) of a long term evolution (LTE)wireless communication system, high power signals can cause measureablePIM due to non-linear behavior of components such as RF transmissioncables, duplexers, connectors, antenna, or some object external to anantenna of the base station.

Passive intermodulation (PIM) distortion is problematic for multi-bandtransmitters when intermodulation distortion (IMD) falls into occupiedreceiver (Rx) channels, which desensitizes the receiver. Multi-bandsignals are an important characteristic of LTE and multi-standardradios, so the occurrence of PIM problems will be more frequent thanwith previous cellular wireless communication standards. There are manycauses of PIM related to materials, manufacturing quality and quality ofworkmanship by installation and maintenance technicians.

A test can be conducted during the installation of a base station todetect sources of PIM. In such a PIM test, one technician monitors thethird order intermodulation distortion (IMD3) of two high power inputsignals, while another person taps and wiggles (dynamic testing) allconnectors, cables and components between the TX port on the radio andthe antenna. Failed PIM tests could be a result of failing components,over or under-tightened connectors, or dirty connectors, including metalflakes. Some PIM sources will not be detected during this test and arelater catalyzed by some change in the environment, e.g., wind, trainvibrations, temperature, etc. Other PIM sources can develop with aging,such as corrosion. If a PIM problem is detected at a base station duringnormal operation, then a crew is sent to identify and remove the PIMsource. In some cases the PIM source may be due to some object externalto the base station like a fence. In this case the PIM source cannot beremoved, so the antenna may need to be re-oriented or the transmit powerdecreased.

In a base station, the high power transmit signal of the base stationtransmitter is typically a source of PIM distortion when the transmitsignal passes through a passive device that exhibits some non-linearity.Therefore, the PIM distortion may be considered a nonlinear function ofthe transmit signal. Several methods have been proposed to estimate PIMdistortion that falls into a band of the desired receive signal. Onesuch method involves multiplying transmitted signals to generate 2^(nd)and higher order IMD products. Complex weights are then applied to eachIMD product in a manner that reduces the PIM distortion in the receiverpass band. This approach models the PIM source with a polynomial model,and passes the transmit signal through the polynomial model to estimatethe PIM distortion in the receiver pass band.

In another approach, an output signal of the power amplifier (PA) of thetransmitter is tapped and fed to an auxiliary receiver, called acancellation receiver. The cancellation receiver is tuned to the desiredreceiver pass band. The signal content in the receiver pass band at thePA output is presumed to be due to intermodulation products (IMPs) fromthe transmit signals caused by non-linear behavior of the PA. These IMPsin the receiver pass band are then adaptively filtered in thecancellation receiver so as to match the PIM signal at the output of themain receiver. The estimate of the PIM in the cancellation receiver issubtracted from the output of the main receiver.

A problem with these two approaches is that their models are trainedwith a PIM signal that is typically weaker than the uplink signal, evenwhen the uplink signal is only noise and in-band interference. Further,both of these approaches require provision of an additional receiver.

SUMMARY

The embodiments described herein advantageously provide a method andsystem for detecting intermodulation distortion (IMD) affecting areceived signal in a wireless receiver. According to one aspect,embodiments include a method for intermodulation distortion detection.The method includes determining a measurement indicative ofintermodulation distortion based on at least one transmit signal. Whenthe measurement indicative of intermodulation distortion exceeds a firstpre-determined level, at least one sample of an amplitude of a signaloutput by the wireless receiver is collected in a first data set. Whenthe measurement indicative of intermodulation distortion does not exceeda second pre-determined level, the second predetermined level being lessthan the first predetermined level, at least one sample of an amplitudeof the signal output by the wireless receiver is collected in a seconddata set. A comparison is performed based on data of the first data setand on data of the second data set to determine a measure ofintermodulation distortion.

According to this aspect, in some embodiments, an expected delay of theat least one transmit signal observed by the wireless receiver isdetermined to determine which of the at least one sample to include inone of the first and second data sets. In some embodiments, a time ofcollecting at least one sample in one of the first data set and thesecond data set is determined based on an estimated delay associatedwith an intermodulation distortion source. In some embodiments, themeasurement indicative of intermodulation distortion is based on aninstantaneous amplitude of an Nth order product of transmit signals. Insome embodiments, the measurement indicative of intermodulationdistortion is an instantaneous value of a product of baseband values oftwo transmit signals and the first pre-determined level is a specifiedlevel greater than an average value of the product of the basebandvalues. In some embodiments, the measurement indicative ofintermodulation distortion is an instantaneous value of a product ofbaseband values of two transmit signals and the second pre-determinedlevel is specified level less than an average value of the product ofthe baseband values. In some embodiments, the comparison is a comparisonof a mean value of the first data set to a mean value of the second dataset. In some embodiments, the method includes generating a firststatistical distribution based on data of the first data set, andgenerating a second statistical distribution based on data of the seconddata set. The comparison is then a comparison of the first statisticaldistribution and the second statistical distribution. In someembodiments, an extent to which the first statistical distribution andthe second statistical distribution differ indicates an extent ofintermodulation distortion. In some embodiments, the comparison is acomparison of a calculated mean square difference between the firststatistical distribution and the second statistical distribution to athreshold. In some embodiments, the method also includes generating athird statistical distribution based on data in a third data set, thedata in the third data set being collected when the measurementindicative of intermodulation distortion exceeds a third predeterminedlevel when the receiver output has a second average received signalpower that is different from a first average received signal powerexisting during collection of data of the first data set. In theseembodiments, the method further includes generating a fourth statisticaldistribution based on data in a fourth data set, the data in the fourthdata set being collected when the measurement indicative ofintermodulation distortion does not exceed a fourth pre-determined levelwhen the receiver output has the second average received signal power.In some embodiments, the method is performed without disabling livetraffic into the receiver.

According to another aspect, the embodiments include an apparatus fordetecting intermodulation distortion affecting a received signal in awireless receiver. The apparatus includes a memory and a processor. Thememory is configured to store a first data set that includes samples ofan amplitude of a receiver signal collected when a measurementindicative of intermodulation distortion exceeds a first pre-determinedlevel. The memory is further configured to store a second data set thatincludes samples of the amplitude of the receiver signal collected whenthe measurement indicative of intermodulation distortion does not exceeda second pre-determined level, the second pre-determined level beingless than the first pre-determined level. The processor is incommunication with the memory and is configured to collect the samplesof the first data set when the measurement indicative of intermodulationdistortion exceeds the first pre-determined level and to collect thesamples of the second data set when the measurement indicative ofintermodulation distortion does not exceed the second pre-determinedlevel. The processor is further configured to perform a comparison basedon data of the first data set and on data of the second data set todetermine a measure of intermodulation distortion.

According to this aspect, in some embodiments, the processor is furtherconfigured to determine an expected delay of transmit signals observedby a wireless receiver to determine which samples to include in each ofthe first and second data sets. In some embodiments, a time ofcollecting a sample is determined based on an estimated delay associatedwith an intermodulation distortion source. In some embodiments, themeasurement indicative of intermodulation distortion is based on aninstantaneous amplitude of an Nth order product of transmit signals. Insome embodiments, the measurement indicative of intermodulationdistortion is an instantaneous value of a product of baseband values oftwo transmit signals and the first pre-determined level is a specifiedlevel greater than an average value of the product of the basebandvalues. In some embodiments, the measurement indicative ofintermodulation distortion is an instantaneous value of a product ofbaseband values of two transmit signals and the second pre-determinedlevel is a specified level less than an average value of the product ofthe baseband values. In some embodiments, the comparison is a comparisonof a mean value of the first data set to a mean value of the second dataset. In some embodiments, the processor is further configured to:generate a first statistical distribution based on data of the firstdata set, and generate a second statistical distribution based on dataof the second data set. In these embodiments, the comparison is acomparison of the first statistical distribution and the secondstatistical distribution. In some embodiments, an extent to which thefirst statistical distribution and the second statistical distributiondiffer indicates an extent of intermodulation distortion.

According to yet another aspect, embodiments include a receiver equippedto determine a condition of intermodulation distortion. The receiverincludes a detector module configured to detect a measurement indicativeof intermodulation distortion. The receiver also includes a collectormodule configured to collect in a first data set samples of a receiversignal amplitude when the measurement indicative of intermodulationdistortion exceeds a first pre-determined level and to collect in asecond data set samples of the receiver signal amplitude when themeasurement indicative of intermodulation distortion does not exceed asecond pre-determined level, the second pre-determined level being lessthan the first pre-determined level. The receiver also includes acomparator module configured to perform a comparison based on data ofthe first data set and data of the second data set to determine ameasure of intermodulation distortion.

According to this aspect, in some embodiments, the receiver furtherincludes a transmit module configured to transmit at least one transmitsignal, a receiver module configured to receive a signal arising fromthe at least one transmit signal, and a delay determination moduleconfigured to determine an expected delay between the at least onetransmit signal and the receiver signal to determine which samples toinclude in each of the first and second data sets. In some embodiments,the receiver further includes a statistical distribution generationmodule configured to generate a first statistical distribution based ondata in the first data set collected by the collector module and togenerate a second statistical distribution based on data in the seconddata set collected by the collector module. In these embodiments, thecomparator module performs a comparison of the first statisticaldistribution and the second statistical distribution. In someembodiments, the comparator module is further configured to indicateremedial action to correct intermodulation distortion when the first andsecond statistical distributions are substantially different.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present embodiments, and theattendant advantages and features thereof, will be more readilyunderstood by reference to the following detailed description whenconsidered in conjunction with the accompanying drawings wherein:

FIG. 1 is a block diagram of a radio configured according to principlesset forth herein;

FIGS. 2-6 are graphs of statistical distributions representing datacollected during conditions favorable and unfavorable for IMD fordifferent values of a ratio of an uplink signal power to a PIM power;

FIG. 7 is a block diagram of an IMD detector constructed in accordancewith principles described herein; and

FIG. 8 is a flowchart of an exemplary process of detecting IMD in aradio receiver.

DETAILED DESCRIPTION

Before describing in detail example embodiments that are in accordancewith the present disclosure, it is noted that the embodiments resideprimarily in combinations of apparatus components and processing stepsrelated to detection of intermodulation distortion such as passiveintermodulation distortion affecting a receiver in a radio. Accordingly,the system and method components have been represented where appropriateby conventional symbols in the drawings, showing only those specificdetails that are pertinent to understanding the embodiments of thepresent disclosure so as not to obscure the disclosure with details thatwill be readily apparent to those of ordinary skill in the art havingthe benefit of the description herein.

As used herein, relational terms, such as “first” and “second,” “top”and “bottom,” and the like, may be used solely to distinguish one entityor element from another entity or element without necessarily requiringor implying any physical or logical relationship or order between suchentities or elements.

When a radio receiver of a base station receives a desired signal from awireless device, the radio receiver may also receive intermodulationdistortion (IMD) due to passive intermodulation (PIM). Note that as usedherein, IMD includes, but is not limited, to PIM. As explained below,methods of detecting PIM may be employed to detect IMD, generally, suchas IMD from a transmitter of the base station. Thus, where detection ofPIM is described herein, the description and application of methods andapparatus described herein may apply more generally to IMD.

Embodiments described herein detect a presence of PIM in the receivedsignal. In particular, the received signal may be sampled to generate afirst data set during conditions that are favorable for PIM and may besampled to generate a second data set during conditions that areunfavorable for PIM. Conditions that are unfavorable for PIM exist whenthe signals that generate the PIM have low instantaneous power levels atthe PIM source. Conditions that are favorable for PIM exist when thesignals that generate the PIM have high instantaneous power levels atthe PIM source. The signals that generate the PIM are the transmitsignals of a radio transmitter of the base station. The transmit signalsare known and are used to determine when there are favorable orunfavorable conditions for PIM.

In some embodiments, a statistical comparison of the first and seconddata set may be performed to determine a measure of intermodulationdistortion. For example, a mean value of the data of the first data setcan be compared to a mean value of the data of the second data set. Anextent to which the two mean values differ indicates an extent ofintermodulation distortion. Thus, if the two mean values are similar,IMD is considered to be low. If the two mean values differsubstantially, IMD is considered to be high. As another example, avariance of the data of the first data set can be compared to a varianceof the data of the second data set to determine an extent ofintermodulation distortion.

In some embodiments, a first statistical distribution may be obtainedfrom the first data set and a second statistical distribution may beobtained from the second data set. The two statistical distributions maythen be compared. If the two statistical distributions are significantlydifferent, then the received signal has a component that is dependent onthe instantaneous amplitudes of the transmitted signal, indicatingsignificant intermodulation distortion. Conversely, if the twostatistical distributions are very similar, then any IMD from thetransmitter is much smaller than the received signal, which means thatif PIM exists, the PIM is low enough to be non-problematic. Thus, forexample, a calculated mean square difference between the firststatistical distribution and the second statistical distribution may becompared to a threshold. An extent to which the threshold is exceededmay be used to indicate an extent of intermodulation distortion.

\Referring now to the drawing figures, there is shown in FIG. 1 a blockdiagram of a radio 10 for detecting intermodulation distortion in areceive module 12. The radio 10 includes the receive module 12, atransmit module 14, a duplexer 16, an antenna 18 and an intermodulationdistortion (IMD) detector 20. The transmit module 14 receives a signalto be transmitted that may include a single band signal or two or morebands of signals separated by frequency spacings, i.e., a multi-bandsignal. For example, the transmit signal may include one or moreorthogonal frequency division multiplex (OFDM) signals and/or one ormore wide band code division multiple access (WCDMA) signals. Thetransmit module 14 amplifies the input signal and may also applypre-distortion to compensate for the non-linearity of a power amplifierof the transmit module 14. The output signal of the transmit module 14is fed to the duplexer 16 which operates to isolate the output signal ofthe transmit module 14 from entering the receive module 12 and to feedthe output signal of the transmit module 14 to the antenna 18. In thereceive path, a signal received from the antenna 18 is fed to theduplexer 16 which operates to isolate the signal from the antenna 18from entering the transmit module 14 and to feed the signal from theantenna 18 to the receive module 12.

The intermodulation distortion detector 20 samples the transmit signalsthat are input to the transmit module 14 to determine if conditions arefavorable or unfavorable for PIM. For example, the intermodulationdistortion detector 20 may determine that conditions are favorable forPIM when an instantaneous value of a product of baseband values of twotransmit signals exceeds a first pre-determined level. In someembodiments, the first pre-determined level is a specified level greaterthan an average value of the product of the baseband values. Thespecified level may be, for example, 6 dB greater than the averagevalue. The intermodulation distortion detector 20 may determine thatconditions are unfavorable for PIM when the instantaneous value of theproduct of baseband values of the two transmit signals fails to exceed asecond pre-determined level. In some embodiments, the secondpredetermined level is a specified level less than the average value ofthe product of the baseband values. The specified level may be, forexample, 20 dB less than the average value. Although, a product of twotransmit signals is described, a product of more than two transmitsignals may also be employed in determining whether conditions arefavorable or unfavorable for passive intermodulation.

When a condition favorable for PIM is detected, the IMD detector 20 addsa corresponding sample or series of samples of the received signal to afirst data set. When a condition unfavorable for PIM is detected, theIMD detector 20 adds a corresponding sample or series of samples of thereceived signal to a second data set. In one embodiment, a statisticaldistribution is generated for each of the first and second data sets.For example, the statistical distribution could be the probabilitydensity function of the received signal's amplitude. Examples of thesestatistical distributions are shown in FIGS. 2-6.

FIGS. 2-6 are graphs of the probability density function 24 for thefirst data set favorable for PIM and the probability density function 22for the second data set unfavorable for PIM, for different values of theratio of uplink signal power to PIM power at a third orderintermodulation (IMD3) level. In FIG. 2, the ratio is 0 dB. In FIG. 3,the ratio is 6 dB. In FIG. 4, the ratio is 12 dB. In FIG. 5, the ratiois 18 dB. In FIG. 6, the ratio is 24 dB. A simulator was used togenerate a receive signal having an uplink signal as well as PIM causedby two transmit signals. The uplink signal may consist of anycombination of the desired uplink signal, receiver noise, and in-bandinterference.

Referring to FIGS. 2-6, as the ratio of the uplink signal power to PIMpower increases (indicating a lower relative level of PIM), theprobability density functions 22 and 24 merge and ultimately overlap sothat when the ratio is 24 dB, as shown in FIG. 6, the two functions areindistinguishable. Thus, an extent to which the first and secondstatistical distributions differ indicates an extent of intermodulationdistortion. The larger the difference between the distributions, thelarger the intermodulation distortion. In some embodiments, a measure ofthe difference between the statistical distributions may be made bycalculating the mean square difference between the distributions andcomparing the mean square difference to a threshold. An extent to whichthe mean square difference exceeds the threshold is an indication of theextent of IMD.

Referring to FIG. 4, PIM can be detected even when the PIM is 12 dB ormore below the uplink signal. If PIM is detected when the PIM is 12 dBbelow the receive module's noise floor, then the PIM will notsignificantly degrade the receiver performance. In such event, a networkoperator could schedule maintenance on the radio 10 at an advantageoustime, instead of immediately. This is preferable to the alternative ofPIM going unnoticed until the PIM degraded receiver performance to apoint of significant degradation, resulting in lost coverage andcapacity. Thus, embodiments described herein permit detection of PIMbefore the PIM significantly degrades receiver performance.

The time delay between when the transmit signals are sent into thetransmitter and when the corresponding PIM is received in the digitaldomain and manifests itself in the output of the receiver depends on theposition of the PIM source, which is not known a priori, because the PIMcan be due to many different mechanisms. In some embodiments the processof collecting samples for favorable and unfavorable PIM conditions canbe performed for each expected delay of a set of expected delays insuccession, the expected delays being associated with probable PIMsources. The probable PIM sources may be, for example, RF connectors. Insome embodiments, instead of capturing a single sample during acondition favorable or unfavorable for PIM, several consecutive samplesare taken during a window of time to capture the effects over a range ofdelays. All or some of these samples may be used to detect PIM. Forexample, a sample that is the maximum value of all the samples may beselected as the basis for determining PIM.

The processes described herein may be employed during normal operationof the radio or may be employed with the uplink traffic to the receiverdisabled. In some embodiments, when the IMD detection process isemployed during operation of the radio when uplink traffic is notdisabled, the process of collecting samples may be restarted when thestatistical distribution of the uplink traffic changes. In someembodiments, different statistical distributions can be collected fordifferent average received power levels. Thus, for example, a first setof statistical distributions may be generated for data collected whenthe average received power is high, and a second set of statisticaldistributions may be generated for data collected when the averagereceived power is lower. In some embodiments, no change is made even ifthe received signal statistical distribution changes.

In some embodiments, uplink traffic may be disabled during the processof PIM detection. If some PIM is present when the uplink signal isdisabled, the greater will be the difference between statisticaldistributions based on data collected when the uplink traffic isdisabled. This is evident from FIGS. 2-6. PIM detection when the uplinktraffic is disabled may advantageously be employed when PIM is weak. Insome embodiments, a selective application of various test signalsapplied to the transmit module 14 may be employed when testing for PIMwhen the uplink traffic is disabled.

FIG. 7 is a block diagram of an IMD detector 20 configured to collectsamples, and determine a presence of PIM. The IMD detector 20 includes amemory 26 and a processor 28. The memory 26 is configured to store atleast a first data set 30 and a second data set 32. The first data set30 has data that is collected when conditions are favorable for PIM andthe second data set 32 has data that is collected when conditions areunfavorable for PIM.

The processor 28 is configured to perform various functions fordetermining PIM. In some embodiments, the processor 28 executes computercode that causes the processor to execute functions described herein. Insome embodiments, the processor 28 is application specific integratedcircuitry configured to perform the functions described herein. Thus, insome embodiments, the detector module 34, the collector module 36, thedistribution generation module 38, the comparator module 40 and thedelay determination module 42 are software modules, whereas in otherembodiments, some or all of these modules are implemented in specifichardware circuitry.

The detector module 34 of the processor 28 functions to detectconditions favorable or unfavorable for PIM. For example, the detectormodule 34 may sample the transmit signals being submitted to thetransmit module 14 and determine that a condition favorable to PIMexists when a product of instantaneous amplitudes of input transmitsignals exceed a first threshold and determine that a conditionunfavorable to PIM exists when the product falls below a secondthreshold lower than the first threshold.

The collector module 36 of the processor 28 functions to collect samplesof the output of the receive module 12 during conditions determined bythe detector module 34 to be favorable for PIM and store the collectedsamples in the first data set 30. The collector module 36 also functionsto collect samples of the output of the receive module 12 duringconditions determined by the detector module 34 to be unfavorable forPIM and store these samples in the second data set 32.

In some embodiments, the processor 28 may include a distributiongeneration module 38 that functions to generate statisticaldistributions based on the data collected by the collector module 36.For example, a statistical distribution may be a probability densityfunction. These statistical distributions may serve as a basis fordetermining a presence of PIM. Note it is contemplated that not allembodiments have a distribution generation module 38, but may insteadhave a moment generation module (not shown) to generate moments of thedata, such as a mean value and/or variance.

A comparator module 40 of the processor 28 functions to perform acomparison based on the data of the first data set 30 and the seconddata set 32 collected by the collector module 36. In some embodiments,for example, the comparator module 40 may compare a mean value of eachdata set. If the mean values are similar, a determination of low PIM maybe made, whereas, if the mean values differ substantially, adetermination of high PIM may be made. A low PIM may be, for example,below 18 dB lower than the uplink signal power, and a high PIM may be,for example, above 12 dB below the uplink signal power. In someembodiments, the comparator module 40 may compare attributes ofstatistical distributions generated by the distribution generationmodule 38 based on the two data sets to determine an extent of PIM.

A delay determination module 42 of the processor 28 functions todetermine a delay or group of delays associated with one or more PIMsources. A delay is the time it takes for a transmit signal to go intothe radio 10, generate PIM and then be observed by the receive module12. The determined delay or group of delays determine the timing forcollecting the samples of the first and second data sets.

FIG. 8 is a flowchart of an exemplary process of determining thepresence of PIM in a radio. A measurement indicative of IMD isdetermined by the detector module 34 (block S100). This measurement maybe, for example, an instantaneous amplitude of a product of transmitsignals being input to the transmit module 14. In some embodiments, themeasurement indicative of intermodulation distortion is based on aninstantaneous amplitude of an Nth order product of transmit signals. Forexample, a third order product of transmit signals may be defined as aproduct of a square of an amplitude of a signal in a first band times anamplitude of a signal in a second band. If the signal of the first bandis at frequency f1 and the signal of the second band is at frequency f2,then the third order product will be at 2f1-f2, where f2 is greater thanf1. The measurement indicative of IMD may be compared to a firstthreshold (block S102). This threshold may be, for example, a specifiedlevel above the average value of the amplitude of the product oftransmit signals, thereby indicating a condition favorable for PIM. Ifthe measurement exceeds the first threshold, a sample or group ofsamples of the output of the receive module 12 is collected in the firstdata set by the collector module 36 (block S104). A time of collectionof data for the first data set may be based on determination of a delayor delays associated with one or more PIM sources, as determined by thedelay determination module 42.

If the measurement does not exceed the first threshold, a determinationis made whether the measurement falls below a second threshold (blockS106). The second threshold may be, for example, a specified level belowthe average value of the amplitude of the product of transmit signals,thereby indicating a condition unfavorable for PIM. If the measurementfalls below the second threshold, a sample or group of samples of theoutput of the receive module 12 is collected in the second data set bythe collector module 36 (block S108). A time of collection of data forthe second data set may be based on determination of a delay or delaysassociated with one or more PIM sources, as determined by the delaydetermination module 42. If the measurement does not fall below thesecond threshold, then a determination is made whether data collectionis complete (block S110). Data collection may end based on the totalnumber of data samples collected, for example. If data collection is notcomplete, the process returns to block S100. If data collection iscomplete, a comparison is performed by the comparator module 40 based onthe first and second data to determine an extent of IMD (block S112).

Note that although reference is made herein to favorable and unfavorableconditions for PIM, any two different conditions may be used. Forexample, conditions indicative of medium PIM and strong PIM could beused. In some embodiments the conditions to be used are indicative ofvery weak PIM, such as below 18 dB below uplink signal power, and verystrong PIM, such as above 0 dB above uplink signal power. Note also,that in addition to detecting passive intermodulation (PIM), embodimentsmay also be employed to detect intermodulation distortion (IMD)generated in the transmit module 14, which if detected, could beremedied. Further, as noted above, determination of an extent ofintermodulation distortion based on data collected in the first andsecond data sets can be performed in different ways, including comparinga mean or variance of the data of the data sets or generating andcomparing statistical distributions of the data of each data set. Alsonote that the detection measurements for determining a condition of PIMmay be based on the amplitude of a single input transmit signal or basedon a product of amplitudes of two or more input transmit signals.

An advantage of embodiments described herein is that no model of PIM isrequired or assumed. Also, the PIM can be detected even when the PIM ismuch weaker than the received signal. Further, testing is possibleduring normal radio operation without disabling the uplink traffic.However, in some embodiments, the uplink traffic may be disabled fordetermining PIM. Embodiments enable detection and repair of PIM beforePIM reaches the point of significant receiver degradation.

As will be appreciated by one of skill in the art, the conceptsdescribed herein may be embodied as a method, data processing system,and/or computer program product. Accordingly, the concepts describedherein may take the form of an entirely hardware embodiment, an entirelysoftware embodiment or an embodiment combining software and hardwareaspects all generally referred to herein as a “circuit” or “module.”Furthermore, the disclosure may take the form of a computer programproduct on a tangible computer usable storage medium having computerprogram code embodied in the medium that can be executed by a computer.Any suitable tangible computer readable medium may be utilized includinghard disks, CD-ROMs, electronic storage devices, optical storagedevices, or magnetic storage devices.

Some embodiments are described herein with reference to flowchartillustrations and/or block diagrams of methods, systems and computerprogram products. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer program instructions. These computer program instructions maybe provided to a processor of a general purpose computer, specialpurpose computer, or other programmable data processing apparatus toproduce a machine, such that the instructions, which execute via theprocessor of the computer or other programmable data processingapparatus, create means for implementing the functions/acts specified inthe flowchart and/or block diagram block or blocks.

These computer program instructions may also be stored in a computerreadable memory or storage medium that can direct a computer or otherprogrammable data processing apparatus to function in a particularmanner, such that the instructions stored in the computer readablememory produce an article of manufacture including instruction meanswhich implement the function/act specified in the flowchart and/or blockdiagram block or blocks.

The computer program instructions may also be loaded onto a computer orother programmable data processing apparatus to cause a series ofoperational steps to be performed on the computer or other programmableapparatus to produce a computer implemented process such that theinstructions which execute on the computer or other programmableapparatus provide steps for implementing the functions/acts specified inthe flowchart and/or block diagram block or blocks.

It is to be understood that the functions/acts noted in the blocks mayoccur out of the order noted in the operational illustrations. Forexample, two blocks shown in succession may in fact be executedsubstantially concurrently or the blocks may sometimes be executed inthe reverse order, depending upon the functionality/acts involved.Although some of the diagrams include arrows on communication paths toshow a primary direction of communication, it is to be understood thatcommunication may occur in the opposite direction to the depictedarrows.

Computer program code for carrying out operations of the conceptsdescribed herein may be written in an object oriented programminglanguage such as Java® or C++. However, the computer program code forcarrying out operations of the disclosure may also be written inconventional procedural programming languages, such as the “C”programming language. The program code may execute entirely on theuser's computer, partly on the user's computer, as a stand-alonesoftware package, partly on the user's computer and partly on a remotecomputer or entirely on the remote computer. In the latter scenario, theremote computer may be connected to the user's computer through a localarea network (LAN) or a wide area network (WAN), or the connection maybe made to an external computer (for example, through the Internet usingan Internet Service Provider).

Many different embodiments have been disclosed herein, in connectionwith the above description and the drawings. It will be understood thatit would be unduly repetitious and obfuscating to literally describe andillustrate every combination and subcombination of these embodiments.Accordingly, all embodiments can be combined in any way and/orcombination, and the present specification, including the drawings,shall be construed to constitute a complete written description of allcombinations and subcombinations of the embodiments described herein,and of the manner and process of making and using them, and shallsupport claims to any such combination or subcombination.

It will be appreciated by persons skilled in the art that theembodiments described herein are not limited to what has beenparticularly shown and described herein above. In addition, unlessmention was made above to the contrary, it should be noted that all ofthe accompanying drawings are not to scale. A variety of modificationsand variations are possible in light of the above teachings withoutdeparting from the scope of the following claims.

What is claimed is:
 1. A method of detecting intermodulation distortionaffecting a received signal in a wireless receiver, the methodcomprising: determining a measurement indicative of intermodulationdistortion based on at least one transmit signal; when the measurementindicative of intermodulation distortion exceeds a first pre-determinedlevel, collecting at least one sample of an amplitude of a signal outputby the wireless receiver in a first data set; when the measurementindicative of intermodulation distortion does not exceed a secondpre-determined level, the second predetermined level being less than thefirst predetermined level, collecting at least one sample of anamplitude of the signal output by the wireless receiver in a second dataset; performing a comparison based on data of the first data set and ondata of the second data set to determine a measure of intermodulationdistortion to be mitigated; and causing the intermodulation distortionin the received signal to be mitigated based on the determined measureof the intermodulation distortion.
 2. The method of claim 1, furthercomprising determining an expected delay of the at least one transmitsignal observed by the wireless receiver to determine which of the atleast one sample to include in one of the first and second data sets. 3.The method of claim 1, wherein a time of collecting at least one samplein one of the first data set and the second data set is determined basedon an estimated delay associated with an intermodulation distortionsource.
 4. The method of claim 1, wherein the measurement indicative ofintermodulation distortion is based on an instantaneous amplitude of anNth order product of transmit signals.
 5. The method of claim 1, whereinthe measurement indicative of intermodulation distortion is aninstantaneous value of a product of baseband values of two transmitsignals and wherein the first pre-determined level is a specified levelgreater than an average value of the product of the baseband values. 6.The method of claim 1, wherein the measurement indicative ofintermodulation distortion is an instantaneous value of a product ofbaseband values of two transmit signals and wherein the secondpre-determined level is specified level less than an average value ofthe product of the baseband values.
 7. The method of claim 1, whereinthe comparison is a comparison of a mean value of the first data set toa mean value of the second data set.
 8. The method of claim 1, furthercomprising: generating a first statistical distribution based on data ofthe first data set; and generating a second statistical distributionbased on data of the second data set, wherein the comparison is acomparison of the first statistical distribution and the secondstatistical distribution.
 9. The method of claim 8, wherein, an extentto which the first statistical distribution and the second statisticaldistribution differ indicates an extent of intermodulation distortion.10. The method of claim 8, wherein the comparison is based on comparinga calculated mean square difference between the first statisticaldistribution and the second statistical distribution to a threshold. 11.The method of claim 8, further comprising: generating a thirdstatistical distribution based on data in a third data set, the data inthe third data set being collected when the measurement indicative ofintermodulation distortion exceeds a third predetermined level when thereceiver output has a second average received signal power that isdifferent from a first average received signal power existing duringcollection of data of the first data set; and generating a fourthstatistical distribution based on data in a fourth data set, the data inthe fourth data set being collected when the measurement indicative ofintermodulation distortion does not exceed a fourth pre-determined levelwhen the receiver output has the second average received signal power.12. The method of claim 1, wherein the method is performed withoutdisabling live traffic into the receiver.
 13. An apparatus for detectingintermodulation distortion affecting a received signal in a wirelessreceiver, the apparatus comprising: a memory configured to store: afirst data set that includes samples of an amplitude of a receiversignal collected when a measurement indicative of intermodulationdistortion exceeds a first pre-determined level; a second data set thatincludes samples of the amplitude of the receiver signal collected whenthe measurement indicative of intermodulation distortion does not exceeda second pre-determined level, the second pre-determined level beingless than the first pre-determined level; and a processor incommunication with the memory and configured to: collect the samples ofthe first data set when the measurement indicative of intermodulationdistortion exceeds the first pre-determined level; collect the samplesof the second data set when the measurement indicative ofintermodulation distortion does not exceed the second pre-determinedlevel; perform a comparison based on data of the first data set and ondata of the second data set to determine a measure of intermodulationdistortion to be mitigated; and cause the intermodulation distortion inthe receiver signal to be mitigated based on the determined measure ofthe intermodulation distortion.
 14. The apparatus of claim 13, whereinthe processor is further configured to determine an expected delay oftransmit signals observed by a wireless receiver to determine whichsamples to include in each of the first and second data sets.
 15. Theapparatus of claim 13, wherein a time of collecting a sample isdetermined based on an estimated delay associated with anintermodulation distortion source.
 16. The apparatus of claim 13,wherein the measurement indicative of intermodulation distortion isbased on an instantaneous amplitude of an Nth order product of transmitsignals.
 17. The apparatus of claim 13, wherein the measurementindicative of intermodulation distortion is an instantaneous value of aproduct of baseband values of two transmit signals and wherein the firstpre-determined level is a specified level greater than an average valueof the product of the baseband values.
 18. The apparatus of claim 13,wherein the measurement indicative of intermodulation distortion is aninstantaneous value of a product of baseband values of two transmitsignals and wherein the second pre-determined level is a specified levelless than an average value of the product of the baseband values. 19.The apparatus of claim 13, wherein the comparison is a comparison of amean value of the first data set to a mean value of the second data set.20. The apparatus of claim 13, wherein the processor is furtherconfigured to: generate a first statistical distribution based on dataof the first data set; and generate a second statistical distributionbased on data of the second data set, wherein the comparison is acomparison of the first statistical distribution and the secondstatistical distribution.
 21. The apparatus of claim 20, wherein, anextent to which the first statistical distribution and the secondstatistical distribution differ indicates an extent of intermodulationdistortion.
 22. A receiver equipped to determine and mitigate acondition of intermodulation distortion, the receiver comprising: adetector configured to detect a measurement indicative ofintermodulation distortion; a collector configured to collect in a firstdata set samples of a receiver signal amplitude when the measurementindicative of intermodulation distortion exceeds a first pre-determinedlevel and to collect in a second data set samples of the receiver signalamplitude when the measurement indicative of intermodulation distortiondoes not exceed a second pre-determined level, the second pre-determinedlevel being less than the first pre-determined level; a comparatorconfigured to perform a comparison based on data of the first data setand data of the second data set to determine a measure ofintermodulation distortion to be mitigated; and a corrector configuredto cause the intermodulation distortion in the receiver signal to bemitigated based on the determined measure of the intermodulationdistortion.
 23. The receiver of claim 22, further comprising: atransmitter configured to transmit at least one transmit signal; areceiver configured to receive a signal arising from the at least onetransmit signal; and a delay determiner configured to determine anexpected delay between the at least one transmit signal and the receiversignal to determine which samples to include in each of the first andsecond data sets.
 24. The receiver of claim 22, further comprising astatistical distribution generator configured to generate a firststatistical distribution based on data in the first data set collectedby the collector and to generate a second statistical distribution basedon data in the second data set collected by the collector; and whereinthe comparator performs a comparison of the first statisticaldistribution and the second statistical distribution.
 25. The receiverof claim 24, wherein the comparator is further configured to indicateremedial action to correct intermodulation distortion when the first andsecond statistical distributions are substantially different.